Research On Active Damping Control Strategy To Improve Converter Weak Grid Adaptation

As a key equipment in the field of new energy generation,transmission and power quality management,grid-connected converters are widely used in modern power systems and have become an important feature of power electronic power systems.However,in recent years,the system instability oscillation caused by the interaction between converter and grid is frequent,which seriously threatens the safe operation of the grid and is a key problem to be solved.Therefore,this paper focuses on the active damping control strategy to improve the adaptability of converter weak grids.To address the problem that larger grid equivalent impedance may cause converter instability under weak grid conditions,this paper first derives the Norton equivalent circuit of the converter and analyzes the stability of the system under weak grid using the impedance ratio criterion,and the results show that the robust stability of the system to the grid equivalent inductance is poor.To this end,an active damping control strategy based on band-pass filtering is proposed,which theoretically proves its effectiveness in improving the adaptability of the converter to the weak grid,and further compares the effects of different virtual resistance values on the active damping control effect,so as to give the corresponding parameter selection principles.It should be noted that the above active damping strategy directly using the common coupling point(PCC)voltage as the feedback quantity will weaken the system’s ability to suppress the background harmonic voltage disturbance,which in turn affects the quality of the grid-connected current.To this end,an active damping strategy based on the harmonic differentiation of the grid-connected current is proposed,which converts the resonant current caused by the system instability oscillation into the resonant voltage at the PCC point through the differentiation operation to avoid introducing the background harmonic voltage disturbance to the grid-connected current reference value,and further analyzes the damping control effect theoretically and compares the effect of the two control methods on the system background harmonic voltage disturbance.The results show that the proposed strategy can meet the needs of both stable control of grid-connected converter systems and high-quality grid-connected currents in weak grids.Finally,a simulation model of the grid-connected converter under weak grid is established and an experimental prototype is built under PLECS software.The simulation and experimental results under different operating conditions verify the correctness of the theoretical analysis and the effectiveness of the proposed active damping strategy.